JPH0813155B2 - Indoor digital data wireless communication system and method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is generally directed to indoor digital data radio between stations for communication between the stations and access to various resources connected to the stations. Regarding communication. In a particular disclosed environment, multiple mobile stations communicate with one or more fixed base stations connected to a computer system, such as a local area network. More particularly, the invention relates to a system in which a base station exercises control over access to a wireless channel by periodically broadcasting messages that separate fixed time intervals called "frames." Moreover, such messages subdivide the frame in a variable manner for transmission between the base station and remote stations, allocation of fixed periodic time intervals to various remote stations, and remote It allows flexible time allocation for the three channel usage modes, with the interval at which the station utilizes various contention mechanisms to access the channel.

The subject matter of the invention disclosed in this application is related to the subject matter disclosed in US patent application Ser. No. 07 / 605,285.

[0003]

BACKGROUND OF THE INVENTION Indoor data radio systems are often installed to enable communication between mobile stations and applications and data on computer systems within an enterprise. For example, suppose the company owns a warehouse that stores various stocks. Mobile stations in the form of handheld computers and radio transceivers with bar codes are used to check the quantity of products inventoried, and the data collected in this way is used to enter computer systems. Transmitted to base station.

In a typical architecture, there are a plurality of mobile stations in communication with a fixed station that acts as a gateway or bridge between the wireless environment and a conventional local area network (LAN). The fixed station relays the message to other LAN connection resources. Communication is rarely done directly between mobile stations. Rather, messages are exchanged between applications residing on fixed nodes. In this structure, it is natural to add some radio system management functions to the above gateway management functions, including coordination of mobile station access to common radio channels. This augmented gateway is considered here as the base station.

Providing efficient access to a channel is an important issue in indoor digital data radio systems because the channel is capacity limited and shared by all its users. Static channel allocation means such as frequency division multiplex (FDM) or fixed time division multiplex (TDM) are inefficient for various types of inter-computer traffic that are known to be bursts in nature. is there. On the other hand, other services (eg voice transmission, control applications, etc.) require a fixed upper bound on the maximum latency for channel access that is best satisfied by regular and guaranteed access to the channel. .

Efficient use of wireless channels is a fundamental requirement for practical indoor wireless data networks. The different types of traffic coming from different data terminals are usually bursty in nature and unpredictable. Random access schemes are known for short response times when the channel load is light. As the channel load increases, the random access scheme becomes inefficient and unstable. On the other hand, controlled access schemes such as polling achieve fairly good channel utilization efficiency under heavy load. However, the polling scheme has overhead problems because the polling cycle must be reduced to meet the response time requirements.

Therefore, the protocol of the indoor digital data radio system should have the following characteristics.

(1) When the channel load is light, the access time is short. (2) Channel usage is good when the channel load is heavy.

(3) Unconditionally stable. (4) Easy to execute.

(5) When most of the traffic goes from the base station connected to the LAN to the mobile station, it is in good agreement with the general traffic pattern.

Some forms of indoor data radio are used as "spread spectrum" as approved by the Federal Communications Commission (FCC) in part 15.247 of the Code for use in certain frequency bands without user permission. Utilizes known transmission technology. Spread spectrum communication offers several advantages including a low density power spectrum and interference rejection. There are several spread spectrum systems, including direct sequence digital systems, frequency hopping systems, time hopping systems, pulse frequency modulation (or chirp) systems, and various hybrids. Among these systems,
Direct sequence digital systems and frequency hopping systems are probably more widely implemented than other systems. In direct sequence digital systems, a high speed pseudo-random code generator is used to modulate the slower digital data which in turn modulates the carrier. In a frequency hopping system, a coherent oscillator is created to jump from one frequency to another under the influence of a pseudo-random code generator.

The present invention is implemented using spread spectrum communication systems of either direct sequence digital or frequency hopping type. For a description of these and other types of spread spectrum communication systems, see, for example, "Spread Spectrum Systems, Second Edition."
(Robert C. Dixon, John Wiley & Sons (1984)), and "Spread Spectral Communication Volume 2 (Spread Spect).
rum Communications, Vol. II) "(MK Simon, Co
mputer Science Press (1985)).

[0013]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the response time when the traffic load is light and to increase the channel utilization efficiency when the traffic load is heavy.
It is to provide a protocol for access.

Another object of the invention is to support traffic with latency constraints, to be able to configure the system in different applications with different characteristics, and to be "fair" under heavy load. What can be guaranteed is included.

[0015]

SUMMARY OF THE INVENTION According to the present invention, a spread spectrum communication technique is used to provide a hybrid of controlled and random access schemes. More specifically, the frame is subdivided into two intervals so that various medium access protocols can be utilized at the individual intervals.
In principle any protocol can be used in the two intervals, but in the preferred embodiment of the protocol 1
Central control method is used in one interval, and another one
A decentralized method is used in one interval. The relative lengths of the intervals can be varied to accommodate changing load conditions.

The preferred embodiment of the present invention is implemented using a frequency hopping spread spectrum communication system. Frequency hopping spread spectrum
In the system, the carrier frequency of the transmitter changes at individual time intervals, but is constant from time to time. Periods of constant frequency are called "hops" and messages are exchanged only during these "hops". Because the hops have a finite duration, these hops provide structure on the radio channel. That is, the transmission is unlikely to occur across hop boundaries. Therefore,
Hops give a framing structure over time.

The present invention provides "transparent connectivity" between the customer and the server program in the sense that neither program needs to be aware of the existence of the wireless link. The "configuration" objective of the present invention is achieved by setting boundaries between each interval of system configuration time. Therefore, multiple-dam-terminal
-dumb-terminal) application installs a base station just for polling,
In portable PC (personal computer) applications, the base station is installed only to allow contention access. The "fair" objective of the present invention is achieved by shifting from contention to polling or allocation as load increases, and thus even if a particular remote station is a weaker competitor than other stations. Remote station never "locks out"
Guaranteed not to be.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, in more detail, FIG.
Looking at, an in-room wireless system is shown that enables communication between a plurality of mobile stations 10, 12, 14 and 16 and applications and data resident in a computer system. The computing system includes a local area network (LAN) (denoted by reference numeral 24) server 18 having a plurality of workstations or personal computers (not shown for simplicity) attached thereto. Is common. A monitor 20 and a keyboard 22 are connected to the server 18. Also connected to the LAN are one or more gateways 26 and 28 that communicate with mobile stations 10, 12, 14 and 16. These gateways are considered base stations and are augmented in accordance with the present invention to provide some radio system management functions that coordinate mobile station access to common radio channels.
Communication between mobile stations is based on the base station 2
Supported via relay via 6 and 28.

As shown in more detail in FIG. 1B,
The base station 26 or 28, which is a conventional microcomputer, comprises a LAN adapter 30 which is inserted into a bus slot and connected to a LAN cabling 32. The server 18 is also typically a conventional microcomputer, having one or more direct access storage devices (DASD) (not shown), such as hard disks, inserted into the bus slot and LAN. A LAN adapter 34 connected to the cabling 32 is provided. The LAN adapters 30, 34 and the LAN cabling 32 are combined with LAN software to form the LAN 24.
To form. LAN 24 is of conventional design and does not form part of the present invention. The base station 26 or 28 also includes an RF transceiver adapter 36, which acts as a printed circuit card that is inserted into the bus slot of the base station. The transceiver adapter 36 includes a spread
A spectrum transceiver is included. Transceiver
The adapter 36 has an antenna 38, and this antenna 38
A wireless link 40 with one or more remote or mobile stations 10, 12, 14 or 16.
Is established. The mobile station is a handheld or laptop computer of conventional design. The mobile station, like the base station, is equipped with an antenna 42 and a transceiver adapter 44 implemented as a printed circuit card that is inserted into the bus slot of the computer. Similar to transceiver adapter 36, transceiver adapter 44 includes a spread spectrum transceiver of similar design. In addition, the base station and mobile station are equipped with software, indicated by reference numerals 46 and 48, respectively, which software supports each transceiver adapter.

FIG. 2 shows a radio system common to both the mobile station and the base station of FIG. The wireless system includes a transceiver adapter 36 or 44 connected to the computer 50 via the computer's bus interface 52. The transceiver section is
RF transceiver 54, which is a spectrum transceiver
And a dedicated microprocessor system 56 that controls the transceiver via interface 58. In addition, the microprocessor system 56 includes a transceiver section and a computer section 5
A system interface 60 that interfaces with 0 is included. Also, the microprocessor system is a high-resolution time interval determination hardware that is common in real-time microprocessor systems.
Alternatively, it includes a dedicated microprocessor 62 that includes a "timer".

Microprocessor 62 is connected by a memory bus 64 to interfaces 58 and 60 which provide connections to bus interface 52 and RF transceiver 54, respectively, and also to program storage 66 and data storage 68. It is connected. Program storage 66 is typically read only memory (ROM) and data storage is static or dynamic random access memory (SRAM, or DRA).
M). Packets received or to be transmitted are held in data store 68 and are part of microprocessor 62, direct memory access (DM).
A) RF transceiver 54 via interface 58 under control of a serial channel with a controller (not shown).
Be communicated with. The function of these serial channels is
Encapsulating data and control information within an HDLC (High Level Data Link Control) packet structure and providing serial format packets to the RF transceiver 54.
For more information on the HDLC packet structure, see, for example, Mischa Schwartz, Telecommunication Networks: Protocols, Modeling and Analysis (Telecommun
ication Networks: Protocols, Modeling and Analysi
s) ”(Addison-Wesley (1988)).

When a packet is received via the RF transceiver 54, the serial channel checks the packet's destination address for any further errors and deserializes the packet to the data store 68. To do. The serial channel must have the ability to recognize a particular adapter address as well as the broadcast address. Specific microprocessors with appropriate serial channel and timer functions include Motorola 68302 and Nat
Includes ional HPC46400E microprocessor.

Computer 50 runs an operating system 70 that supports one or more user application programs 72. The operating system 70 includes a communication management program 74, or the communication management program 74 itself is an application program installed on a computer. In either case, the communication management program 74 controls the device driver 76 via the operating system 70. Device driver 7
6 in turn communicates with transceiver adapter 36 or 44 via bus interface 52.

FIG. 3A shows a protocol executed by the present invention. This protocol is equally applicable to radio frequency (RF), infrared (IR) or wired transmission systems with broadcast capability and conventional or spread spectrum modulation techniques, but with slow-frequency-hop. Hopped) spread spectrum wireless systems have a natural resemblance to this protocol because they share structure in a timely manner with this protocol. However, the present invention was implemented using a direct sequence spread spectrum system that is amenable to this protocol.

Referring to FIG. 3A, there are five intervals that define a "hop". First (and last)
G is the interval at which the transmitter carrier frequency is changing. Note that the G-interval is only needed for frequency hopping systems. This interval has a duration H. The next interval X ₁ is the interval in which the base station broadcasts a specific message to all mobile stations identifying the beginning of the next interval, the B interval. A B-interval is by convention a base station only initiates transmissions and a mobile station responds only if required by the message protocol. For example, the mobile station acknowledges the outgoing message from the base or responds if polled. The B interval has a duration T ₁ . In turn, the B interval is followed by the X ₂ interval. The X ₂ interval is the interval in which the base station broadcasts a specific message to all mobile stations identifying the end of the B interval and implicitly the beginning of the C interval. This message also carries the length of the C-interval and, optionally, the length of the B-interval.

The X ₂ broadcast message is not strictly necessary. Information about the entire hop structure may be carried in the X ₁ interval. The X ₂ message is included to assist in the operation of a simplified remote station capable of contention-based operation only. These stations vie after waiting for the X ₂ message.

The C-interval is an interval in which any station including the base station (or optionally excluded) contends for a channel and transmits a message without permission of the base station. For example, C
The SMA / CA (Carrier Sense Multiple Access with Collision Avoidance) protocol is used at this interval. The C-interval has a duration of T ₂ .

The mobile station sends a message,
Upon receipt of the acknowledgment, the message is considered to have been successfully received. Otherwise, the mobile stations will vie again. At the end of the C-interval not sent by the mobile station with the special message is the protection interval. T _msg is the time to transmit a special message, T _ack is the time to transmit an acknowledgment, and T _{ack
If the turnaround} is the time between the end of the transmission of the message and the start of the transmission of the acknowledgment, the protection interval is T _msg + T _ack + T _turnaround . Since T _msg is a function of the length of the message to be transmitted, the protection interval will be different for different mobile stations that have messages to send. The protection interval is not exhausted. Rather, messages and acknowledgments are sent and received all at once until the end of the C-interval.

[0029] By varying the time T _2, the base station or stretching the intervals of contention, it is possible to or shrink. Increasing the time T ₂ is advantageous for mobile response time when the system is very lightly loaded and most of the traffic is going inward to the base station. Conversely, if the system is heavily loaded and most of the traffic is going out, then time T ₂ should be minimized. However, the time T ₂ should not be reduced to zero. This is because the time T ₂ is the only mechanism used by the newly activated mobile station to register itself with the base station.

Further, the B-interval in which the traffic between the remote and the base is carried in the allocated time slot is further subdivided as shown in FIG. 3 (B).
In FIG. 3B, the B-interval is further subdivided into subintervals of B ₁ and B ₂ , and then the B ₂ subinterval is further subdivided into a plurality of time slots, each time slot being a specific remote station. Assigned to. B ₁
In response to polling during subinterval, the remote
A request is issued by the station for its assigned slot or during the C-interval. Once confirmed by the message from the base station, the slot assignment ensures that the remote station will transmit to the base station during its assigned time slot.

By changing the boundary between the B ₂ subinterval and the C interval, the suitability of the system for different types of traffic can be adjusted.
As the traffic load for stable and predictable traffic (eg, real-time audio and video) increases, its boundaries are moved to extend the B ₂ subinterval and shorten the C interval, which The number of time slots that can be allocated can be increased. Conversely, as traffic becomes unpredictable, its boundaries are moved to extend the C-interval, giving contention-based traffic more bandwidth.

From FIG. 3A, a "hop" is divided into two subdivisions, one supporting a controlled random access scheme and the other supporting a random access scheme. I understand. The present invention is 3
It is operated in one of two modes: one in which only X ₁ messages are sent, _{one in which} only X ₂ messages are sent, and one in which both these two messages are sent.

In the mode where only X ₁ messages are sent, the X ₁ messages make up the header section of the frame. This header section identifies the beginning of the information frame, carries a single identifier of the base station, identifies the frequency hopping pattern, and also defines the length of the B and C intervals. Also, X ₁
The messages optionally carry general broadcast and system control information.

In operation, each mobile station has an X₁Me
Wait for sage. Once received, the mobile station
When the contention interval begins,
I know when to schedule the next frequency change
Sea urchin, T₁And T₁+ T₂Set an internal timer for
I do. Reception of broadcast messages is not guaranteed
Yes. The radio condition is that the specific mobile station broadcasts
Sage X₁It is a condition not to listen to. Mobile station
First X₁Listen to the message ₁Through
If you don't let it pass, you cannot voluntarily transmit.
It remains silent to the body. Or move
The station is the base station during interval B.
Be polled by the
However, there is no competition in the C interval. Mobile station
The last frame so that you know when to hop
To T₁+ T₂Need to remember the X₁Message
Listen in the next frame for Ji. If X₁Message
Ji was not heard in many consecutive frames
The mobile station with the rest of the system.
I lost sync and didn't think I was in sync mode
Don't

Each frame time of length T = T ₁ + T ₂ is also
Frequency hopping time for execution under FCC Part 15 A fixed length of time T is recommended but not required. The fixed length of time T is particularly useful when:

(1) A fixed length of time T makes interference separation more feasible when several frequency hopping patterns are used in the overlapping operation of a multi-cell radio system. In this case, the frequency hopping pattern information in the header section can be used to identify the hopping sequence for the mobile terminal that follows.

(2) If all radios in the system hop to the same pattern, then the fixed length of time T is that different cells are in different phases of the hopping pattern:
Allows synchronous hops. This eliminates interference between cells.

In choosing the length of time T, a trade-off needs to be made. If the time T is long, the system
There is less overhead, and a shorter time T results in less system response time.

X₁Instead of a message, the system uses X
₂Only messages can be transmitted. X ₂Message content
Is X₂The mobile station receiving the message is immediately
Except that you can start contention on
X₁It can be the same as the content of the message. this
Is an advantage in some applications.

If only X ₂ messages are to be transmitted,
Suppose the base station polls the mobile station near the end of the B-interval and that this mobile station responds with a long message (generally the protocol must prohibit these responses from being too long). The response may become active just when the time T ₁ has elapsed. This is a problem for X ₁ messages only, but for X ₂ messages:
The base station sends X _{2 as} soon as the response is complete.
Issue a message and see that the X ₂ message contains the shortened time T ₂ . The effect is to reduce the contention interval for the duration of one hop.

In a third mode of operation, X ₁ to simplify the implementation of the mobile station and to provide redundancy.
Both messages and X ₂ messages can be used. The X ₁ message then signals the beginning of the B interval. The X ₂ message also signals the beginning of the C interval.

In a particular implementation of the invention, only X ₁ messages were used. An advantage of X ₁ message for X ₂ message for the mobile station to power down the receiver to X ₁ message is expected to save power, it is that it is possible to know the time of occurrence of X ₁ message . It also reduces the susceptibility of X-type messages to spurious reception. Combining X ₁ and X ₂ messages is the most secure and straightforward to implement in a mobile station. For mobile stations with only contention,
Only X ₂ messages can provide some simplicity.

The dynamic adjustment of the relative duration of the B and C intervals as a function of system load is an important feature of the present invention. Since every message contains a base station, the base station
It is possible to record the relative traffic strength (the number of messages) at each of B and C intervals. This recording process is generally performed by continuously executing the tally for the number of messages in each interval for a predetermined time. At the end of that time, the base station evaluates the tally accumulated for each interval and, based on this information and other relevant factors, makes a decision on whether to change the length of each interval. .

As a special case, consider the modified protocol shown in FIG. If there are many messages sent from the base station to the mobile station, the base station can decide to lengthen the B ₁ subinterval and correspondingly shorten the B ₂ subinterval and C interval. On the contrary, if the C-interval is heavily utilized and the mobile station does not have much demand on the allocated slot, then the C-interval can be lengthened at the expense of the B ₂ subinterval.

The length of the B1 interval need only be long enough to use up the base station's transmission queue for a particular frame, so the base station dynamically adjusts this subinterval length for each frame. Can be changed to. Base station is X ₁
At the time the message is broadcast, the length of the B ₁ subinterval must be evaluated. This evaluation is based on the number and length of messages in the transmission queue at the beginning of the frame.

Other measures of traffic need to be considered by the base station. For example, B ₂
The decision to lengthen the subinterval is very effective when made based on the number of outstanding slot allocation requests made by the mobile station. In addition, the mobile station monitors the delays (or collisions experienced by the mobile station) experienced in its attempt to use the C-interval, and checks for periodic requests from the base station for status or of the packet itself. Report this information to the base station as a field.
In addition, the base station can determine the average transmission queue length for itself and all active remote stations. The queue length for the remote station can be determined by periodic reporting or by including the queue length in every packet transmitted to the base station. .

FIGS. 4A and 4B, taken together, represent a flow diagram showing the logic for adjusting the length ratio of the B ₁ , B ₂ subintervals and C intervals. Source of a suitable computer language (eg, C, Pascal, BASIC, etc.) supported by the base station
The code can be written from the flow chart by a computer programmer familiar with the particular computer language used.

Referring to FIG. 4A, the process begins by the system initialization routine process, during which the tally counters for the B ₁ , B ₂ subintervals and C intervals are set to zero and the time The counter is preset to a predetermined time. Next, the functional block 80
At, the tally counter is advanced for the message during each interval of the B ₁ , B ₂ subintervals and the C interval. The time timer is periodically checked at decision block 82, and when the time timer expires,
The number of messages in the base station's transmission queue is checked at function block 86. In addition, the base station checks, at function block 88, the delay reported by the mobile station. The information so accumulated, i.e. the real number of messages for each interval, the relative number of messages between intervals, the length of the transmission queue, and the delay reported by the mobile station, will need to be adjusted at each interval. Used to determine Adjustment criteria are determined empirically for a particular application. A test is performed at decision block 90 to determine if the adjustment criteria are met. If not, the tally counter and time timer are reset at function block 92 before the process loops back to function block 80.

If the adjustment criteria are met, the process is as shown in FIG.
Proceed to (B). In FIG. 4B, a series of tests is performed. The first test is performed at decision block 94 to determine if subinterval B ₁ should be changed.
If so, adjustments are made at function block 96. Next, a test is performed at decision block 98 to determine if the subinterval B ₂ should be changed. If so, adjustments are made in function block 100. Finally, the test is performed at decision block 102,
Determine whether the interval C should be changed. If so, adjustments are made in function block 104.
At this point, as shown by the D connector, FIG.
When (A), the process returns to the function block 92.

The above description assumes that the mobile station is synchronized with the base station.
Describes the process by which a mobile station first establishes a connection with a base station. Slow frequency hops, which are generally more difficult to synchronize
cy-hopped) system is described.

In any system, the mobile station is
A priori knowledge of a range of carrier frequencies that can also be used
have. For example, the 915 MHz ISM band
In (902-928MHz), the low-speed frequency hop (S
LH) system has a maximum channel width of 0.5MHz
And 52 channels separated by 0.5 MHz
give. After completing various initial setup steps,
A mobile station that wants to connect to a station
Tunes its receiver to one of the available channels.
Let X₁Or X₂Wait for message. For example,
Up length is T₁+ T ₂Move if + H = 50 ms
The average time a station has to wait is 52
× 50 × 0.5 = 1300 milliseconds, that is, 1.3 seconds
You. X₁Or X₂When you receive the message, the mobile station
From the content of the message,
, Base station identifier, and hopping
Know the turn. Then the mobile station
On the next hop, change the receiver frequency appropriately₁
Or X₂Wait for a message. After doing a few hops,
All, or almost all X₁Or X₂message
Is received normally, the mobile station
Declare that it is in sync with the station. Consecutive hot
Enough X₁Or X₂No message received
After that, the mobile station becomes the base station or
To reacquire an alternate base station,
Return to wave number listening mode.

Referring to FIGS. 5A and 5B,
The logic of the base station program executing the protocol is shown in flow chart form. This flow chart is
It is for a modified protocol as shown in FIG. 3 (B). Those skilled in the art will recognize that simpler alternative protocols may be easily implemented based on the modified protocol logic. Source code written in a suitable computer language, such as C, Pascal, BASIC, etc., is supported by the base station and can be written from a flow chart by a computer programmer familiar with the particular computer language described above.

In FIG. 5A, the process is started by the system initialization routine process and then enters phase B. At the start of Phase B _1, as shown in function block 106, phase DN is set to Phase B _1, a timer is set for the Phase B ₁ duration, further, a message X ₁ is broadcast It In function block 108, messages to various mobile stations are transmitted from the transmission queue and acknowledgments are received from the polled mobile stations. Periodically, the phase timer is checked at decision block 110 to determine if the time has expired. If not, the process loops back to function block 108 to continue processing message transmissions from the transmission queue.

If the phase timer expires, then phase B ₂ is started by setting the phase identifier to B ₂ in function block 112 and setting the timer for the B ₂ duration. As shown in function block 114, the received message is placed in a receive queue and an acknowledgment is transmitted to the mobile station where the message was received. Periodically, the phase timer is checked at decision block 116 to determine if the timer has expired. If not, the process loops back to function block 114 to continue message receive processing.

If the phase timer has expired, the process is as shown by connector A in FIG.
Proceed to (B). In function block 118, phase C is started at the top of FIG. 5B by setting the phase identifier to C and the timer to the duration of the C interval. The base station then transmits at function block 120 an X ₂ broadcast message notifying the mobile station of the start of the C-interval.

During the C-interval, as indicated by function block 122, messages received from mobile stations are placed in a receive queue and an acknowledgment is transmitted to those mobile stations from which the message was received. Mobile stations that have transmitted messages and have not received an acknowledgment consider these messages not yet received. In this case, the message is held in the mobile station's transmission queue for retransmission during the next frame. Periodically, decision block 1
At 24, the phase timer is checked to determine if the timer has expired. If not, the process continues to function block 122 to continue the process of receiving the message from the mobile station.
Loop back to.

If the timer has expired, then at function block 126 hop processing is performed during the G interval. This process is performed according to the scheduled broadcast of the X ₁ message. Next, functional block 128
At, the process proceeds to phase B ₁ and the same protocol is repeated during the next frame.

As shown in the flow charts of FIGS. 6A and 6B, the software for the mobile station is similar. First, after initializing the system, at function block 130 the system waits for an X ₁ message. When the X ₁ message is received, in function block 132 the phase identifier is set to B ₁ and the timer duration is also set to the B ₁ interval. During this interval, at function block 134, the message received from the base station is stored in the receive queue and an acknowledgment is sent to the base station. Periodically, at function block 136, the phase timer is checked to determine if the timer has expired. If not, the process loops back to function block 134 to continue receiving messages that may be transmitted by the base station.

If the timer has expired, then in function block 138 the process identifies the phase identifier B.
Phase B ₂ is entered by setting it to ₂ and setting the timer to the B ₂ interval duration. Next, at function block 140, a slot timer is set to the beginning of the time slot allocated for the mobile station. The system waits for the slot timer at decision block 142 and continues to FIG. 6B as indicated by the B connector, and if the slot timer has expired, at function block 144 the mobile station Send a message from the message queue and receive an acknowledgment from the base station. The system then waits for the phase timer at decision block 146.

As defined in decision block 148,
When X ₂ broadcast message is received, the phase C starts. The X ₂ broadcast message is sent to decision block 14
Expected after the phase timer has expired in 6. In the mobile station, function block 15
0, set the phase identification name to C,
Phase C is initiated by setting the timer to the phase duration and the slot timer to a random multiple of the slot width. Phase C is, for example, Mi
The slotted ALOHA protocol is implemented as described in the above reference by scha Schwartz. next,
At decision block 152, the system waits for the slot timer. In response to the slot timer, at function block 154, the mobile station transmits from the transmission queue and receives an acknowledgment. As mentioned above, the mobile station considers the message not received if it does not receive an acknowledgment. In such a case,
The message is held in the transmission queue for transmission processing during the next frame. The system then waits for the phase timer at decision block 156. Phase
If the timer expires, at function block 158, X
Hop processing is performed according to the data received in _one message, and the process proceeds at function block 160 to phase B ₁ for the next frame.

While the present invention has been described by embodiments having various alternatives, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the immediate patent scope. For example, the protocol according to the present invention runs in a distributed file system consisting of remote stations only. One of these remote stations is designated as the base station. In addition, the base station designation is done dynamically if the currently designated base station fails. Therefore, those skilled in the art will recognize that there are other environments in which the protocol according to the present invention may be implemented.

[0062]

Since the indoor digital data radio system of the present invention is configured as described above, it is possible to provide efficient access to the channel.

[Brief description of drawings]

FIG. 1A is a pictorial diagram illustrating an indoor wireless digital data communication system of the type in which the present invention is implemented.
FIG. 1B is a block diagram of the system shown in FIG. 1 and illustrates the basic components of the mobile station and base station.

FIG. 2 is a block diagram of a wireless system used to implement the preferred embodiment of the present invention.

FIG. 3A is a data framing diagram showing the protocol implemented by the preferred embodiment of the present invention. (B) is a data framing diagram showing a modification of the basic protocol described in (A).

FIGS. 4A and 4B, when integrated, show a logic flow diagram of a process that allows a base station to adjust intervals as a function of traffic load and other factors.

FIG. 5 (A) and (B), when integrated,
6 shows a logic flow diagram of protocol processing by a station.

6A and 6B, when integrated, show a logic flow diagram of protocol processing by a mobile station.

[Explanation of symbols]

 10, 12, 14, 16 Mobile Station 18 Server 20 Monitor 22 Keyboard 24 Local Area Network (LAN) 26, 28 Gateway, Base Station 30, 34 LAN Adapter 32 LAN Cabling 36 Transceiver Adapter 44 Transceiver Adapter 52 Bus interface 54 RF transceiver 56 Microprocessor system 58 Interface 60 System interface 62 Microprocessor 66 Program storage device 68 Data storage device 70 Operating system 72 Application system 74 Communication management program 76 Device driver

Front Page Continuation (72) Inventor Robert Thomas Kato United States 27609, Grandville Drive, Lari, North Carolina 3040 (72) Inventor Chia Chi Juan United States 10598, Yorktown Heights, NY Chestnut Coat 348 (56) References JP-A-1-132237 (JP, A) JP-A-1-291545 (JP, A) JP-A-59-204338 (JP, A)

Claims (9)

[Claims] 1. An indoor digital data wireless communication system comprising: a plurality of remote stations each including a radio frequency transceiver; and a computer system including a base station having a radio frequency transceiver, the base comprising: The station transceiver is a means for defining a plurality of frames in which messages and data are transmitted over a radio channel, each of said frames being divided into two intervals,
One is for controlled access by the base station, the other is for contention access by the remote station, and for changing the two intervals according to the message traffic load of the system. An indoor digital data wireless communication system including: 2. The indoor digital data wireless communication system of claim 1, wherein the radio frequency transceiver is a spread spectrum transceiver. 3. The one interval for controlled access is further subdivided into two subintervals, and the base station is configured to perform the first subinterval of the two subintervals. Means for polling a remote station, the remote station being the second of the two subintervals for transmission to the base station.
2. The indoor digital data wireless communication system according to claim 1, wherein time slots are allocated by the base station during each subinterval. 4. The means for varying the two intervals comprises means for measuring the number of messages during each interval over a predetermined period of time, and means for comparing the relative number of messages at each interval. The indoor digital data wireless communication system according to claim 1, comprising: 5. The base for indoor digital data wireless communication between a plurality of remote stations each including a radio frequency transceiver and a computer system including a base station having a radio frequency transceiver. A method performed by a station for defining a plurality of frames in which messages and data are transmitted over a wireless channel, the method comprising:
Each of the frames is divided into two intervals, one for controlled access by the base station and one for contention access by the remote station, and a system message. An indoor digital data wireless communication method comprising: changing the two intervals according to a traffic load. 6. The base station broadcasts a message identifying the beginning and duration of the controlled access interval to the remote stations prior to the controlled access interval. The indoor digital apparatus according to claim 5, further comprising:
Data wireless communication method. 7. The remote station, by the base station, prior to the contention access interval, a message identifying the end of the controlled access interval and the duration of the contention access interval. The indoor digital system of claim 5, further comprising the step of broadcasting to the station.
Data wireless communication method. 8. The base station broadcasts a message identifying the beginning of the controlled access interval to the remote stations prior to the controlled access interval, the base station. Broadcast by the station, before the contention access interval, a message identifying the end of the controlled access interval and the duration of the contention access interval to the remote stations. The indoor digital data wireless communication method according to claim 5, further comprising: 9. The base station measures the number of messages during each interval over a period of time; the base station compares the relative number of messages for each interval; The method of claim 5, further comprising: determining by the base station whether to change each of the intervals according to the relative message traffic strength of the interval.